The objective of this research will be to characterize further the mechanism(s) whereby mammary tissue binds H3-cortisol. Competition studies between H3-cortisol and unlabelled steroid hormones and analysis of the data from Scatchard plots will be used extensively to achieve this objective. Experiments using DEAE-cellulose chromatography and antibodies to bovine serum will be conducted to further characterize the similarities between serum and mammary receptors for cortisol. The H3-cortisol-mammary cell complex will be incubated with trypsin and the released radioactivity applied to thin-layer chromatography plates to monitor whether cortisol or its metabolites are specifically bound to mammary tissue. Another objective will be to characterize the specifity, affinity, and number of the binding sites in mammary tissue derived from cattle in different physiological states (calves, pregnant heifers, lactating cows).